Electronic and magnetic structures of the newly synthesized cobalt oxyselenide La2Co2Se2O3 (structurally similar to the superconducting iron pnictides) are studied through density functional calculations. The obtained results show that this material is a Mott insulator, and that it has a very stable Co2+ high-spin ground state with a t2g-like orbital ordering, which is substantiated by the calculated crystal-field excitation energies. The square lattice of the Co2+ spins is found to have a strong antiferro (a weak ferro) magnetic coupling for the second nearest neighbors (2nn) via O (Se2) and an intermediate antiferro one for the 1nn, with the strength ratio about 10:1:3. The present results account for the available experimental data of magnetism, and the prediction of a planar frustrated (2x2) antiferromagnetic structure would motivate a new experiment.
We show that the interplay of a high density two-dimensional electron gas and localized electrons in a neighboring Mott insulator leads to kinetic magnetism unique to the Mott/band insulator interface. Our study is based upon a bilayer Hubbard model at $U=\infty$ with a potential difference between the two layers. We combine analytic results with DMRG simulations to show that magnetism, and especially ferromagnetism, is greatly enhanced relative by the proximity of the two subsystems. The results are potentially relevant to recent experiments suggesting magnetism in $R$TiO$_3$/SrTiO$_3$ hetero…
We study the interplay of strong electron correlations and intra-triangle spin exchange at two-thirds filling of the single-orbital Hubbard model on the decorated honeycomb lattice using rotationally invariant slave bosons. We find that the spin exchange tunes between a spin-$1$ Mott insulator, a metal, and a spin-$0$ Mott insulator when the exchange is antiferromagnetic. The Mott insulators occur from effective intra-triangle multi-orbital interactions and are adiabatically connected to the ground state of an isolated triangle. An antiferromagnetic spin exchange, as determined by the Goodenou…
Quasi-two-dimensional non-collinear magnetism in the Mott insulator Sr$_2$F$_2$Fe$_2$OS$_2$
通过中子粉末衍射、热力学和输运测量研究了Sr $_2$ F $_2$ Fe $_2$ OS $_2$的磁性。准二维磁序在低于$T_N$ = 106（2）K时发展，面内相关长度超过310 Å，面外相关长度仅为17（3）Å。数据与两k结构一致，其中$k_1$ =（1/2，0，1/2）和$k_2$ =（0，1/2，1/2），有序矩为3.3（1）$μ_B$沿k的面内分量取向。这种结构是由正交的AFM链相交的超交换介导的O网站。密度泛函理论（DFT）也指出了这种结构和一个更窄的Fe 3d带比铁磷属元素化物，从电子相关产生一个莫特绝缘体。
The magnetic structure of Ca$_2$MnReO$_6$ double perovskite is investigated by neutron powder diffraction and bulk magnetization, showing dominant non-collinear Mn magnetic moments [$4.35(7)$ $μ_B$] that are orthogonally aligned with the small Re moments [$0.22(4)$ $μ_B$]. $Ab$-initio electronic structure calculations show that the strong spin-orbit coupling for Re $5d$ electrons combined with a relatively modest on-site Coulomb repulsion ($U_{eff}^{Re} \gtrsim 0.6$ eV) is sufficient to render this material insulating. This is a rare example of spin-orbit assisted Mott insulator outside the re…
We provide the first unbiased evidence for a higher-order topological Mott insulator in three dimensions by numerically exact quantum Monte Carlo simulations. This insulating phase is adiabatically connected to a third-order topological insulator in the noninteracting limit, which features gapless modes around the corners of the pyrochlore lattice and is characterized by a $\mathbb{Z}_{4}$ spin-Berry phase. The difference between the correlated and non-correlated topological phases is that in the former phase the gapless corner modes emerge only in spin excitations being Mott-like. We also sho…
We study the effects of electronic correlations on fragile topology using dynamical mean-field theory. Fragile topological insulators (FTIs) offer obstruction to the formation of exponentially localized Wannier functions, but they can be trivialized by adding certain trivial degrees of freedom. For the same reason, FTIs do not host symmetry-protected flow of edge states between bulk bands in cylindrical boundary conditions but are expected to have a spectral flow between the fragile bands and other bands under certain twisted boundary conditions. We here analyze commonly observed effects of st…
We present a new type of colossal magnetoresistance (CMR) arising from an anomalous collapse of the Mott insulating state via a modest magnetic field in a bilayer ruthenate, Ti-doped Ca$_3$Ru$_2$O$_7$. Such an insulator-metal transition is accompanied by changes in both lattice and magnetic structures. Our findings have important implications because a magnetic field usually stabilizes the insulating ground state in a Mott-Hubbard system, thus calling for a deeper theoretical study to reexamine the magnetic field tuning of Mott systems with magnetic and electronic instabilities and spin-lattic…
The Mott insulator is the quintessential strongly correlated electronic state. We obtain complete insight into the physics of the two-dimensional Mott insulator by extending the slave-fermion (holon-doublon) description to finite temperatures. We first benchmark its predictions against state-of-the-art quantum Monte Carlo simulations, demonstrating quantitative agreement. Qualitatively, the short-ranged spin fluctuations both induce holon-doublon bound states and renormalize the charge sector to form the Hubbard bands. The Mott gap is understood as the charge gap renormalized downwards by thes…
We study the topological properties of Bose-Mott insulators in one-dimensional non-Hermitian superlattices, which may serve as effective Hamiltonians for cold atomic optical systems with either two-body loss or one-body loss. We find that in the strongly repulsive limit, the Mott insulator states of the Bose-Hubbard model with a finite two-body loss under integer fillings are topological insulators characterized by a finite charge gap, nonzero integer Chern numbers, and nontrivial edge modes in a low-energy excitation spectrum under an open boundary condition. The two-body loss suppressed by t…
Motivated by recent experiments on the quantum-spin-liquid candidate material LiZn2Mo3O8, we study a single-band extended Hubbard model on an anisotropic Kagome lattice with the 1/6 electron filling. Due to the partial filling of the lattice, the inter-site repulsive interaction is necessary to generate Mott insulators, where electrons are localized in clusters, rather than at lattice sites. It is shown that these cluster Mott insulators are generally U(1) quantum spin liquids with spinon Fermi surfaces. The nature of charge excitations in cluster Mott insulators can be quite different from co…
Spin susceptibility anomaly in cluster Mott insulators on a partially-filled anisotropic Kagome lattice: applications to LiZn2Mo3O8
受量子自旋液体候选材料LiZn 2 Mo 3 O 8最近实验的启发，我们研究了各向异性Kagome晶格上1/6电子填充的单带扩展哈伯德模型.由于晶格的部分填充，需要产生莫特绝缘体，其中电子被定位在簇中，而不是在晶格位置处的位置间排斥相互作用。我们提供了这样的集群莫特绝缘体的例子，并研究金属态和集群莫特绝缘体的各向异性的可果美晶格之间的相变。结果表明，这些团簇莫特绝缘体一般是具有自旋费米面的U（1）量子自旋液体.然而，在不同的集群莫特绝缘体的电荷激发的性质可能是完全不同的，我们表明，存在一种新的集群莫特绝缘体的电荷波动周围的六边形集群诱导的元胞电荷秩序（PCO）。由于PCO的存在，自旋液体团簇莫特绝缘体中的自旋子激发谱被重构，只有1/3的自旋子激发是磁激活的。同一模型的强耦合极限也通过一个Kugel-Khomskii-like模型进行了分析。基于这些结果，我们认为LiZn_2Mo_3O_8有限温度自旋磁化率的反常行为可以用具有PCO的团簇莫特绝缘体的有限温度性质以及自旋子的分形激发来解释.现有的和可能的未来实验LiZn 2 Mo 3 O 8，和其他钼基团簇磁体进行了讨论，根据这些理论预测。
Ultrafast laser pulses can redistribute charges in Mott insulators on extremely short time scales, leading to the fast generation of photocarriers. It has recently been demonstrated that these photocarriers can form a novel $η$--paired condensate at low temperatures, featuring a staggered superconducting pairing field. In this conference paper, we discuss the origin of the $η$--paired hidden phase and its optical response which may be detected in a pump-probe experiment. The hidden phase may be relevant for possible light-induced superconductivity in Mott insulators.
Motivated by the direct observation of electronic phase separation in first-order Mott transitions, we model the interface between the thermodynamically coexisting metal and Mott insulator. We show how to model the required slab geometry and extract the electronic spectra. We construct an effective Landau free energy and compute the variation of its parameters across the phase diagram. Finally, using a linear mixture of the density and double-occupancy, we identify a natural Ising order parameter which unifies the treatment of the bandwidth and filling controlled Mott transitions.
Motivated by recent progress in the realization of artificial gauge fields and $SU(N)$ Mott insulators using alkaline-earth-like atoms in optical lattices, we develop an unbiased $SU(N)$ real-space dynamical mean-field theory (DMFT) approach to study the effect of spin-orbit coupling and onsite Hubbard interaction $U$ on $SU(3)$ fermionic systems. We investigate the behavior of the local magnetization, double occupancies, and the triple occupancy versus the Hubbard interaction across the metal to Mott insulator transition. We map out the magnetic phase diagram in the large-$U$ limit and show t…
We propose a phenomenological understanding of the recently discovered weak Mott insulator in the moiré superlattice of twisted bilayer graphene, especially the emergent superconductivity at low temperature within the weak Mott insulator phase, namely while lowering temperature, the longitudinal resistivity first grows below temperature $T_m$, but then rapidly drops to zero at even lower temperature $T_c$. An emergent superconductor in an insulator phase is very unusual. Here we propose that this phenomenon is due to the pure two-dimensional nature of the bilayer graphene moiré superlattice. W…
"Nonmagnetic" Dimer Mott insulator induced by the coupling of spin with quantum electric dipoles
基于强耦合分析，提出了一个有效的偶极自旋模型，该模型可以解释“自旋液体莫特绝缘体“的可能起源。这个问题与二聚体莫特绝缘体有关，它使人联想到有机三角晶格系统$κ$ Cu $_2$（CN）$_3$，它的无隙自旋液态已经在二聚体轨道上自旋之间交换耦合的几何阻挫（$J$）的背景下讨论过。事实证明，绝缘体中的另一个自由度，二聚体上的{ \it量子电偶极子}，通过库仑相互作用彼此相互作用，并通过偶极-自旋耦合带来对$J$的显著抑制。
To study excitonic effects on high-harmonic generation (HHG) in Mott insulators, we investigate pumped nonequilibrium dynamics in the one-dimensional extended Hubbard model. By employing time-dependent calculations based on the exact diagonalization and infinite time-evolving block decimation methods, we find the strong enhancement of the HHG intensity around the exciton energy. The subcycle analysis in the sub-Mott-gap regime shows that the intensity region of the time-resolved spectrum around the exciton energy splits into two levels and oscillates following the driving electric field. This …
